Semiconductor integrated circuit device

ABSTRACT

A clock-generating circuit for forming internal clock signals by comparing a signal obtained by delaying, through a variable delay circuit, an input clock signal input through an external terminal with the input clock signal through a phase comparator circuit, and so controlling the delay time of the variable delay circuit that they are brought into agreement with each other, wherein the clock-generating circuit and an internal circuit to be operated by the clock signals formed thereby are formed on a common semiconductor substrate, and an element-forming region in which the clock-generating circuit is formed is electrically isolated from an element-forming region in which the digital circuit is constituted on the semiconductor substrate relying upon the element-isolation technology. The power-source passages, too, are formed independently of other digital circuits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor integrated circuitdevice. More particularly, the invention relates to technology that canbe effectively utilized for a semiconductor integrated circuit devicehaving a clock-generating circuit for generating clock signalscorresponding to clock signals supplied through an external terminals,and that can be effectively utilized chiefly for a synchronous dynamicRAM (random access memory).

2. Prior Art

As a semiconductor integrated circuit device having a digital circuitthat operates on clock signals supplied through an external terminal,there has been known a DLL (delay locked loop) which is a circuit forbringing the clock signals supplied through the external terminal intosynchronism with the internal clock signals to increase the frequency ofthe clock signals while preventing reduction in the timing margin causedby a delay relative to the clock signals supplied to the internalcircuit. The DLL is constituted by a variable delay circuit for varyingthe amount of delay and a control circuit for controlling the amount ofdelay. The phase-synchronizing circuits have been disclosed in JapanesePatent Laid-Open Nos. 90666/1990, 55145/1999 and 171774/1998.

SUMMARY OF THE INVENTION

As a variable delay circuit for the DLL, there can be contrived adigital variable delay circuit for varying the amount of delay bychanging over the number of stages of the circuit and an analog variabledelay circuit for varying the amount of delay by changing the drivecurrent to the delay element or by changing the load. As the circuit forcontrolling the amount of delay of the analog DLL by using the analogvariable delay circuit, further, there can be contrived a circuit of thedigital system that executes a digital control operation and a circuitof the analog system which uses a charge pump or the like. Performancesof the DLLs based on the combinations of the circuits can be roughlyclassified as follows:

(1) Digital control digital DLL: consumes a large amount of power,precision is low, short lock-in cycle, intermediate immunity to noise.

(2) Digital control analog DLL: consumes a large amount of power,precision is high, short lock-in cycle, intermediate immunity to noise.

(3) Analog control analog DLL: consumes a small amount of power,precision is high, long lock-in cycle, poor immunity to noise.

The above-mentioned three kinds of DLLs have their features as describedabove, and an analog control analog DLL is arrived at if powerconsumption and precision are pursued. However, the analog control DLLhas defects of a long lock-in cycle and relatively poor immunity tonoise. Even in the digital control DLL, the variable delay circuit isaffected by noise; i.e., immunity to noise is not so good, and improvingthis defect is meaningful. In the analog control circuit, the controlcircuit, too, is affected by noise and it is estimated that immunity tonoise is poorer than that of the digital control circuit.

In a semiconductor integrated circuit device in which the internaldigital circuit is operated by clock signals supplied through anexternal terminal as represented by a synchronous DRAM (dynamic randomaccess memory), it is expected that input/output operation for the bandwidth, i.e., for the data will be demanded in the future. Thus, thereremains a room for improvement for the DLL of either system inconnection with the precision, immunity to noise and lock-in cycle.

This invention provides a semiconductor integrated circuit deviceequipped with a DLL realizing a stable clock-generating operation. Theinvention further provides a semiconductor integrated circuit deviceequipped with a clock-generating circuit that uses a DLL of a highprecision and of a low power consumption. The invention further providesa semiconductor integrated circuit device equipped with aclock-generating circuit constituted by using a DLL which shortens thelock-in cycle yet maintaining a high precision and consuming a smallamount of electric power. The above and other objects as well as novelfeatures of the present invention will become obvious from thedescription of the specification and the accompanying drawings.

Representative examples of the invention disclosed in this applicationwill now be briefly described. That is, the invention is concerned witha clock-generating circuit for forming internal clock signals bycomparing a signal obtained by delaying, through a variable delaycircuit, an input clock signal input through an external terminal withthe input clock signal through a phase comparator circuit, and socontrolling the delay time of the variable delay circuit that they arebrought into agreement with each other, wherein the clock-generatingcircuit and an internal circuit to be operated by the clock signalsformed thereby are formed on a common semiconductor substrate, and anelement-forming region in which the clock-generating circuit is formedis electrically isolated from an element-forming region in which thedigital circuit is constituted on the semiconductor substrate relyingupon the element-isolation technology.

Another representative example of the invention disclosed in thisapplication will be briefly described next.

That is, the invention is concerned with a clock-generating circuit forforming internal clock signals by comparing a signal obtained bydelaying, through a variable delay circuit, an input clock signal inputthrough an external terminal with the input clock signal through a phasecomparator circuit, and so controlling the delay time of the variabledelay circuit that they are brought into agreement with each other,wherein the clock-generating circuit and an internal circuit to beoperated by the clock signals formed thereby are formed on a commonsemiconductor substrate, and an operation voltage is applied to theclock-generating circuit by using a dedicated bonding pad and a leaddifferent from those of the power source passage that applies anoperation voltage to the internal circuit.

A further representative example of the invention disclosed in thisapplication will be briefly described next.

That is, the invention is concerned with a clock-generating circuit forforming internal clock signals by comparing a signal obtained bydelaying, through a variable delay circuit, an input clock signal inputthrough an external terminal with the input clock signal through a phasecomparator circuit, and so controlling the delay time of the variabledelay circuit that they are brought into agreement with each other,wherein the control circuit so controls the variable delay circuit as toreturn the amount of delay back in the reverse direction at a momentwhen the variable delay time has exceeded a target value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a layout of a dynamic RAMaccording to an embodiment of the present invention;

FIG. 2 is a diagram of layout of a DLL analog unit according into theembodiment;

FIG. 3 is a sectional view schematically illustrating the structure ofelements in a semiconductor integrated circuit device according to theembodiment of the invention;

FIG. 4 is a sectional view schematically illustrating the structure ofelements in a semiconductor integrated circuit device according to theembodiment of the invention;

FIG. 5 is a sectional view schematically illustrating the structure ofelements in a semiconductor integrated circuit device according toanother embodiment of the invention;

FIG. 6 is a block diagram illustrating the whole synchronous DRAMaccording to the embodiment of the invention;

FIG. 7 is a block diagram illustrating the whole DLL according to theembodiment of the invention;

FIG. 8 is a circuit diagram illustrating a variable delay circuitincluded in the DLL analog unit according to t embodiment;

FIG. 9 is a circuit diagram illustrating a charge pump circuit includedin the DLL analog unit according to the embodiment;

FIG. 10 is a circuit diagram illustrating an output amplifier includedin the DLL analog unit according to the embodiment;

FIG. 11 is a circuit diagram illustrating a control voltage-fixingcircuit included in the DLL analog circuit according to the embodiment;

FIG. 12 is a diagram of waveforms illustrating the operation of theclock-generating circuit according to the invention;

FIG. 13 is a diagram of waveforms illustrating the operation of theclock-generating circuit according to the invention;

FIG. 14 is a diagram illustrating the transition of state of a statecontrol circuit included in the clock-generating circuit according tothe invention;

FIG. 15 is a circuit diagram illustrating a phase comparator in the DLLand the state control circuit according to the embodiment;

FIG. 16 is a circuit diagram illustrating a pulse-generating circuit inthe DLL according to the embodiment;

FIG. 17 is a circuit diagram illustrating a pulse-generating circuit inthe DLL according to another embodiment;

FIG. 18 is a circuit diagram illustrating a ¼ frequency divider in theDLL;

FIG. 19 is a circuit diagram illustrating a charge pump testpulse-generating circuit in the DLL according to the embodiment;

FIG. 20 is a plan view illustrating a relationship between the memorychip and the lead frame in the semiconductor integrated circuit deviceaccording to the invention; and

FIG. 21 is a circuit diagram illustrating an electrostatic protectioncircuit in the semiconductor integrated circuit device according to theembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram schematically illustrating the layout of anembodiment of a dynamic RAM to which the invention is applied. In FIG.1, the circuit blocks are formed on a semiconductor substrate such as ofa single crystalline silicon according to a known technology forproducing semiconductor integrated circuits. The circuits in FIG. 1 aredrawn on the semiconductor substrate to nearly meet the geometricalarrangement. In this embodiment, the memory cell array 1 as a whole isdivided into four to constitute memory banks (bank 0 to bank 3).

Peripheral circuits 12 inclusive of an address input circuit, a decodercircuit and a control circuit, a data input circuit (Din buffer) 10, aswell as a data output circuit (Dout buffer) 7, DQS buffer 8 and asequence of bonding pads 11, are provided in the central portion alongone direction of the chip. In a broad sense, the data input circuit 10and the data output circuit 7 are included in the peripheral circuit 12.That is, it should be noted that the data input circuit 10, data outputcircuit 7 and DQS buffer 8 are shown as representative examples of theperipheral circuits. In this embodiment, the peripheral circuits in theabove-mentioned broad sense are arranged to be in parallel with thesequence of bonding pads in order to ideally lay out the circuits suchas random logic circuit and the like circuits.

When, for example, the sequence of bonding pads and the peripheralcircuits are linearly arranged in parallel in the central portion alongone direction of the semiconductor chip, limitation is imposed on thenumber of the bonding pads, and the distance increases for connectingthe bonding pads to the peripheral circuits. In this embodiment, theperipheral circuits are arranged in parallel with the sequence ofbonding pads. In this constitution, the sequence of bonding pads arearranged at positions deviated from the center line which runs in onedirection of the semiconductor chip. As a result, a relatively largearea is maintained in the central portion along one direction of thesemiconductor chip, enabling the layout of the circuit elements to befavorably designed. That is, even in the constitution in which theperipheral circuits are arranged in parallel with a the sequence ofbonding pads as in this application, the degree of integration can beenhanced and the speed of operation can be increased compared with whenthe peripheral circuits are arranged being divided into the right sideand the left side with the bonding pads as a center.

The dynamic RAM of this embodiment is directed to the double data rate(DDR) synchronous DRAM (SDRAM) that will be described later, and theperipheral circuits 12 include data output circuit 7, DQS output circuit8, data input circuit 10 that are described above as representativeexamples, as well as the circuits that will be described below. Abooster circuit forms a boosted voltage VPP higher than the power-sourcevoltage VDD by utilizing a charge pump circuit, and includes a selectioncircuit for selecting a word line to which a memory cell is connectedand a control circuit which determines the selection level for theoperation voltage of the circuit for selecting the shared switchingMOSFET and for controlling the operation of the booster circuit.

A VDD/2 circuit forms a voltage obtained by dividing the power-sourcevoltage VDD by 2 and forms a reference voltage of the input buffer whichis constituted by a differential circuit. The output control circuitcontrols the operation corresponding to the CAS latency of the dataoutput circuit 7. A Y-predecoder decodes a Y-address signal to form apredecoded signal. The read/write buffer controls the operation of themain amplifier and operates the write amplifier.

The input circuit of the address system includes an address buffer, anX-address latching circuit and a Y-address latching circuit. AY-clock-generating circuit generates clock signals corresponding to theoperation of the Y-system upon receiving clock signals supplied throughan external terminal. A mode decoder/clock buffer and a command circuitform operation control signals. A Y-counter and a control circuitthereof are provided to form Y-system address signals in the burst mode.A refresh control circuit executes an automatic/self refreshingoperation, and includes a refresh address counter. There are furtherprovided a bonding option circuit and a power source circuit closuredetector circuit.

The bonding pads are formed being nearly linearly arranged along theplural circuit blocks. According to this constitution, the signaltransmission paths among the circuit blocks do not become undesirablylong avoiding the bonding pads but are formed short to accomplish ahigh-speed operation as compared with those in which the peripheralcircuits are arranged being separated to the right and left sidessandwiching the bonding pads therebetween. Since a circuit block can beformed in a concentrated manner in a substantially large area, thecircuit elements can be easily laid out by taking the automatic wiringinto consideration as will be described later.

In this embodiment, the clock-generating circuit (DLL analog) 3 isprovided nearly at the center of the memory chip. The clock-generatingcircuit is constituted by an analog circuit that will be describedlater. There are further provided a circuit for supplying an inputsignal and a control signal to the above analog circuit, and a digitalcircuit 4 for producing an internal clock signal.

In this embodiment, the four memory cell arrays 1 that are hatched areformed in the triple wells for which the substrate voltage is setseparately from the peripheral circuits 12, thereby to control athreshold voltage for the n-channel MOSFETs that constitute addressselection MOSFETs of memory cells in the memory cell array 1, tosuppress the leakage current to maintain the time for holding the data,and to suppress a change thereof.

The memory cell array 1 is provided with a sense amplifier (Sense AMP) 2which also exists in the triple well in which the memory cell array 1 isformed. The sense amplifier is not geometrically arranged at oneposition only on the semiconductor substrate. In practice, the memorycell array is divided into plural regions depending upon thehierarchical word lines and the hierarchical IO lines, and the senseamplifiers are arranged in a dispersed manner so as to be correspondedto the divided sub-arrays. The DLL analog unit 3 is provided in thetriple well at the center of the memory chip. The triple well in the DLLanalog unit 3 is isolated from the triple well that includes the memorycell array 1 and the sense amplifier 2. A DLL digital unit 4 is providedadjacent to the DLL analog unit 3, so as to be located on the outside ofthe triple well.

In this embodiment, a pair of DLL-dedicated power source pads 5 areprovided near the DLL analog unit 3. The DLL-dedicated power source pads5 are connected to the DLL analog unit 3 only to prevent theinfiltration of power source noise from other circuit blocks through thepower source passage. That is, the DLL-dedicated power source pads 5 areconnected to the DLL analog unit 3 only, and receive no noise from thepower source wiring that supplies operation voltage to the peripheralcircuits 12, to the data output circuit 7 and to the sense amplifier 2,or from the GND wiring.

A DQS buffer 8 is provided neighboring the data output circuit (Doutbuffer) 7. A replica delay circuit (replica delay) 9 is providedneighboring the output buffer 7. The replica delay circuit is used as adelay circuit for bringing a clock signal that has passed through theDQS buffer into precise synchronism with the clock signal suppliedthrough the external terminal.

FIG. 2 is a diagram illustrating the layout of the DLL analog unit 3according to the embodiment. The DLL analog unit 3 is formed in anindependent triple well. In FIG. 2, the periphery of the DLL analog unit3 is hatched to express that the DLL analog unit is formed in a triplewell. The DLL analog unit 3 is provided with dedicated power source padsVDD_DLL (PAD) and VSS_DLL (PAD) for supplying operation voltages such asVDd and VSS, which are corresponding to the pads 5 in FIG. 1.

Though there is no particular limitation, a variable delay circuit 303is constituted by an analog delay circuit which changes the delay timedepending upon a change in the operation current which changes dependingupon the analog control voltage. The variable delay circuit 303 isconstituted by plural stages of delay circuits and is provided withoutput amplifiers (AMP) 305. The variable delay circuit 303 has six setsof output taps connected to the input terminals of the separate outputamplifiers (AMP) 305. Among the six output amplifiers (AMP) 305, onlyone output amplifier is operating at all times, and the outputs of theoutput amplifiers 305 that are not in operation exhibit a highimpedance. Therefore, the output terminals of the six output amplifiers305 are connected in common, and only the output signal of the outputamplifier 305 that is in operation is effectively used. The number ofthe output taps and of the output amplifiers is not limited to six onlybut may be arbitrarily selected.

In this embodiment, though there is no particular limitation, pluralPMOS capacitors constituted by using a p-channel MOSFET are provided inthe outer periphery of the DLL analog unit 3. These PMOS capacitors areused for holding the control voltage, for smoothing the power sourceVDD-GND, and as spare capacitors. In FIG. 2, the PMOS capacitors formedsandwiching the variable delay circuit 303 and the output amplifiers 305therebetween, are connected in parallel by wirings indicated by a solidline in FIG. 2, and are charged and discharged by a charge pump 307 soas to form a control voltage VB. The delay time of the variable delaycircuit is controlled by this control voltage VB.

The PMOS capacitors provided on the outer side of the DLL analog unit 3,except the PMOS capacitor used as the charge pump 307, are used forsmoothing the power source VDD-VSS (GND). This stabilizes the powersource voltage VDD and ground potential VS applied to the circuits thatconstitute the DLL analog unit 3. That is, the smoothing capacitors areconnected between the DLL-dedicated power source pads, i.e., between theVDD_VLL pad and the VSS_DLL pad.

In this embodiment, input buffers 301 that receive control signals fedfrom a unit outside the DLL analog unit 3 are provided in the triplewell. Further, an input buffer 302 is provided in the triple well tosupply a clock input signal ECLK fed through the external unit to thevariable delay circuit 303. Moreover, a CLK output buffer 304 isprovided in the triple well to output a clock output QCL from the wselected output amplifier 305 to the data output circuit 7. In thisconstitution, the phase of the signal QCLK is controlled by the controlvoltage VB that is output as the charge pump 307 is driven by thecontrol signal.

In this embodiment, the variable delay circuit 303 and the charge pump307 susceptible to noise are arranged at the center in the triple wellmaintaining a distance from the surrounding noise sources to prevent theinfiltration of noise. The control signal from the external unit is oncepassed through the buffer in the DLL analog unit 3 to prevent theinfiltration of noise transmitted being superposed on the controlsignal. The DLL-dedicated power source is connected to the DLL analogunit 3, and does not receive noise that infiltrates through the powersource wiring and VSS (GND) wiring. As described above, the variabledelay circuit 303 is provided with six output taps to select any one ofthe six output amplifiers 305 and, hence, to select the number of stagesof the variable delay circuits. This makes it possible to accomplish theadjustment even when the range of variable delay is outside the desiredvalue.

FIG. 3 is a sectional view schematically illustrating the structure ofelements in the semiconductor integrated circuit device according to theembodiment of the invention, and is a cross section along the line a-a′of FIG. 1. As shown, the DWELL including a memory cell array 1 and theDWELL including the DLL analog unit 3 are electrically insulated by thePN junction isolation. Therefore, despite the circuits are formed on thesame p-type substrate PSUB, noise from the sense amplifier 2 which is alarge source of noise is prevented from infiltrating through thesubstrate PSUB.

Further, the substrate power source for the DWELL that includes thememory cell array 1 and for the DWELL that includes the DLL analog unit3, has bonding pads and leads that are exclusively provided, and doesnot receive noise generated in the power source passage. Concretelyspeaking, the power source pads and VSS pad are exclusively provided forthe DLL analog unit 3, and are wire-bonded to dedicated external leads.When the DLL analog unit 3 is used as a voltage-dropping power source, apower source circuit dedicated to the DLL analog unit is provided inaddition to the power source pads and the leads.

FIG. 4 is a sectional view schematically illustrating the structure ofelements in the semiconductor integrated circuit device according to theembodiment of the invention, and is a sectional view along the line b-b′of FIG. 1. The peripheral circuits 12 inclusive of the DLL digital unit4 are formed in the well regions NWELL and PWELL on the p-type substratePSUB on the outer side of the triple WELL, preventing noise due todigital signals from infiltrating into the DLL analog unit 3 through thesubstrate PSUB. In this embodiment, the signals from the DLL digitalunit 4 to the DLL analog unit 3 are passed through the input buffer inthe DLL analog unit, preventing the noise components included in thedigital signals from infiltrating into the charge pump or the variabledelay circuit.

FIG. 5 is a sectional view schematically illustrating the structure ofelements in the semiconductor integrated circuit device according toanother embodiment of the invention, which is a modified embodimentcorresponding to b-b′ of FIG. 1. In this embodiment contrary to that ofFIG. 4, the peripheral circuits 12 inclusive of the DLL digital unit 4are arranged in the triple WELL, and the DLL analog unit 3 is disposedon the outer side of the triple well. The peripheral circuits and theDLL analog unit 3 in the substrate are insulated by the elementisolation technology based upon the triple well. In this case, too,therefore, the infiltration of noise is prevented. The above twoembodiments are the same in a meaning that the peripheral circuitsincluding the DLL digital unit 4 are electrically isolated from the DLLanalog unit 3 by the element isolation technology based on the triplewell. In this case, the triple well including the memory cell array 1 isisolated from the triple well that includes the peripheral circuits.This is because, the memory cell array 1 is disposed in the triple wellin order to apply the substrate potential independently of others ratherthan to cope with the noise.

In the analog control analog DLL of this embodiment, the variable delaycircuit 303 and the charge pump (analog control circuit) 307 aresusceptible to noise. Therefore, these two circuits are isolated fromthe surrounding noise sources. In the DRAM which includes noise sourcessuch as sense amplifiers (Sense AMP) as well as many noise sources inthe periphery, in particular, the separation from the noise sourcesoffers a large effect. As will be described later, further, there isemployed a new system for driving the charge pump which is an analogcontrol circuit, and contrivance is made to eliminate an insensitiveband which is the defect of PFD in the conventional drive system and toshorten the lock-in cycle.

The isolation of the DLL circuit from other circuits offers particularlydistinguished effect in the analog control analog DLL. However, noisegenerated in the chip can also be effectively shut off even in thedigital control digital DLL and in the digital control analog DLL,making it possible to enhance the immunity of the DLL against the noise.That is, even in the digital DLL, when the operation voltage applied tothe inverter circuit constituting the delay circuit varies due to noisein the power source, the charge-up current for the capacitive load andthe discharge current undergo a change in response thereto, resulting ina change in the delay time.

That is, the power-source voltage VDD and the ground voltage VSS areused as a substrate bias voltage for the MOSFET and cause a change inthe threshold voltage and, further, causes a change in the input signalapplied across the gate and the source of the MOSFET. Thus, since boththe input voltage and the threshold voltage are subject to change due tonoise on the power source voltage and on the ground line, the delay timehas changed so far in the conventional digital DLL and, as a result,jittering (fluctuation in the phase) has occurred in the output clocksignals. Upon applying the invention of the application to aclock-generating circuit which uses DLL, therefore, the DLL exhibitsimproved immunity against noise; i.e., jittering of the DLL can bedecreased under the same noise condition or jittering from othercircuits can be more absorbed.

FIG. 6 is a block diagram illustrating an embodiment of the whole DDRSDRAM (double data rate synchronous dynamic random access memory) towhich the invention is applied. Though there is no particularlimitation, the DDR SDRAM of this embodiment is provided with fourmemory arrays 200A to 200D to correspond to the four memory banks. Thememory arrays 200A to 200D corresponded to the four memory banks 0 to 3are equipped with dynamic memory cells arranged in the form of a matrix.In FIG. 6, the terminals for selecting memory cells arranged along thesame column are coupled to the word lines (not shown) of every column,and the data input/output terminals of the memory cells arranged alongthe same row are coupled to complementary data lines (not shown) ofevery row.

Among the word lines (not shown) in the memory array 200A, one word lineis driven to a selection level depending upon the result of decoding therow address signal by the row decoder (row DEC) 201A. The complementarydata lines (not shown) of the memory array 200A are coupled to the I/Olines of the sense amplifier (sense AMP) 202A and of the columnselection circuit (column DEC) 203A. The sense amplifier 202A detectsand amplifiers a very small potential difference appearing on thecomplementary data lines as the data is read out from the memory cells.A column selection circuit 203A therein includes a switching circuit forselecting the complementary data lines and for rendering thecomplementary I/O lines to be conductive. The column switching circuitis selectively operated depending upon the result of decoding the columnaddress signal by the column decoder 203A.

Similarly, memory arrays 200B to 200D, too, are provided with rowdecoders 201B to D, sense amplifiers 203B to D and column selectioncircuits 203B to D. The complementary I/O lines are provided in commonfor the memory banks, and are connected to the output terminals of thedata input circuit (Din buffer) 210 having a write buffer and to theinput terminals of the data output circuit (Dout buffer) 211 having amain amplifier. Though there is no particular limitation, the terminalDQ is a data input/output terminal for inputting or outputting data D0to D15 consisting of 16 bits. A DQS buffer (DQS buffer) 215 forms a datastrobe signal of data output from the terminal DQ.

The address signals A0 to A14 supplied through the address inputterminal are once held by an address buffer 204. Among the addresssignals input in time series, row address signals are held by a rowaddress buffer 205 and column address signals are held by a columnaddress buffer 206. A refresh counter 208 generates a row address at thetime of automatic refreshing and self refreshing operations.

When the device has a storage capacity of, for example, 256 megabits,the column address signals are such that, when a memory access is to beexecuted in a unit of two bits, an address terminal is provided toreceive an address signal A14. In the case of the ×4 bit constitution,signals of up to an address signal All are effectively used. In the caseof the ×8 bit constitution, signals of up to an address signal A10 areeffectively used and in the case of the ×16 bit constitution, signals ofup to an address signal A9 are effectively used. In the case of thestorage capacity of 64 megabits, signals of up to the address signal A10are effectively used in the ×4 bit constitution, signals of up to theaddress signal A9 are effectively used in the ×8 bit constitution, andsignals of up to the address signal A8 are effectively used in the ×16bit constitution as shown.

The output of the column address buffer 206 is supplied as a preset datafor the column address counter 207. The column address counter 207 sendsthe column address signal which is the preset data or a value obtainedby successively increasing the column address signal, to the columndecoders 203A to 203D on a burst mode specified by a command that willbe described later.

A mode register 213 holds various operation mode data. Among the rowdecoders 201A to D, only those corresponding to the bank specified by abank select circuit 212 work to select the word line. Though there is noparticular limitation, a control circuit (control logic) 209 receivesexternal control signals such as clock signal CLK, /CLK (signal having asymbol/means that it is a row enable signal), clock enable signal CKE,chip select signal /CS, column address strobe signal /CAS, row addressstrobe signal /RAS and a write enable signal /WE, as well as /DM, DQSand an address signal through a mode register 213. Based upon a changein the levels of these signals and timings, the control circuit 209forms an internal timing signal for controlling the operation mode ofDDR SDRAM and for controlling the operation of the circuit blocks, andis provided with an input buffer for the signals.

The clock signals CLK and /CLK are input to the DLL circuit 214 that wasdescribed above via a clock buffer to generate internal clocks. Thoughthere is no particular limitation, the internal clocks are used as inputsignals to the data output circuit 211 and to the DQS buffer 215.Further, the clock signals supplied through the clock buffer are fed tothe clock terminal so as to be supplied to the data input circuit 210and to the column address counter 207.

Other external input signals become significant in synchronism with therising edges of the internal clock signals. The chip select signal /CSinstructs the start of a command input cycle depending upon its lowlevel. The chip select signal /CS having a high level (chip non-selectedstate) and other inputs have no meaning. However, the state of selectingthe memory bank and the internal operation such as burst operation thatwill be described later, are not affected by a change into thenon-selected state. Signals /RAS, /CAS and /WE have functions differentfrom the corresponding signals in an ordinary DRAM, and becomesignificant in defining a command cycle that will be described later.

The clock enable signal CKE is the one for instructing the validity ofthe next clock signal. The rising edge of a next clock signal CLKbecomes effective when the signal CKE has a high level, and becomesinvalid when the signal CKE has a low level. In the read mode, when anexternal control signal /OE is provided for controlling the outputenable for the data output circuit 211, the signal /OE, too, is suppliedto the control circuit 209. When the signal /OE has the high level, thedata output circuit 211 assumes a high output impedance state.

The row address signal is defined by the levels A0 to A11 in the rowaddress strobe bank active command cycle that will be described laterand is in synchronism with the rising edge of the clock signal CLK(internal clock signal).

The address signals A12 and A13 are regarded as bank selection signalsin the row address strobe/bank active command cycle. That is, one memorybank is selected out of the four memory banks 0 to 3 depending upon thecombination of A12 and A13. Though there is no particular limitation,the control operation for selecting the memory bank is carried out byactivating the row decoder only on the side of the selected memory bank,by selecting none of the column switching circuits on the side of thenon-selected memory bank, or by the connection to the data input circuit210 and to the data output circuit on the side of the selected memorybank only.

In the case of the ×16 bit constitution with 256 megabits as describedabove, the column address signal can be defined by the levels A0 to A9in the read or write command (column address read command or columnaddress write command described later) cycle in synchronism with therising edge of the clock signal CLK (internal clock). The thus definedcolumn address is used as a start address of burst access.

Next, described below are principal operation modes of the SDRAMinstructed by the command.

(1) Mode Register Set Command (Mo)

This is a command for setting the mode register 30. The command isdesignated by the signals /CS, /RAS, /CAS and /WE=low level, and thedata to be set (register set data) is given through A0 to A11. Thoughthere is no particular limitation, the register set data are burstlength, CAS latency and write mode. Though there is no particularlimitation, the burst length that can be set is 2, 4 or 8, the CASlatency that can be set is 2 or 2.5, and the write mode that can be setis a burst write or a single write.

The CAS latency instructs how may cycles of internal clock signals beused from the break of /CAS to the output operation of the output buffer211 in the reading operation instructed by a column address read commandthat will be described later. The internal operation time is necessaryfor reading the data until the reading data is defined, and is setdepending upon the frequency of the internal clock signals. In otherwords, when internal clock signals of a high frequency are used, the CASlatency is set to a relatively large value and when internal clocksignals of a low frequency are used, the CAS latency is set to arelatively small value.

(2) Row Address Strobe/Bank Active Command (Ac)

This is a command for effectively instructing the row address strobe andfor effectively selecting the memory bank by A12 and A13, and isinstructed by the signals /CS, /RAS=low level, and by the signals /CAS,/WE=high level. At this moment, addresses supplied to A0 to A9 arefetched as row address signals, and signals supplied to A12 to A13 arefetched as memory bank selection signals. The fetching operation isexecuted in synchronism with the rising edge of the internal clocksignals as described above. For example, when the command is designated,a word line is selected in a memory bank that is designated thereby, anda memory cell connected to the word line is rendered conductive to thecorresponding complementary data lines.

(3) Column Address/Read Command (Re)

This is a command necessary for starting the burst read operation andfor instructing the column address strobe, and is instructed by thesignals /CS, /CAS=low level and signals /RAS, /WE=high level. At thismoment, the column addresses supplied to A0 to A9 (in the case of the×16 bit constitution) are fetched as column address signals. The columnaddress signals thus fetched are supplied as burst start addresses tothe column address counter 207.

In the thus instructed burst read operation, the memory bank and theword line therein have already been selected in the row addressstrobe/bank active command cycle, and the memory cells of the selectedword lines are successively selected and are continuously read outaccording to the address signals output from the column address counter207 in synchronism with the internal clock signals. The number of datacontinuously read out is the number designated by the burst length.Reading the data from the output buffer 211 is started after havingwaited for the number of cycles of the internal clock signals specifiedby the CAS latency.

(4) Column Address/Write Command (Wr)

This command is instructed by the signals /CS, /CAS, /WE=low level andby the signal /RAS=high level. At this moment, addresses supplied to A0to A9 are fetched as column address signals. In the burst write, thecolumn address signals thus fetched are supplied as burst startaddresses to the column address counter 207. The procedure of the thusinstructed burst write operation is the same as that of the burst readoperation. However, the write operation includes no CAS latency, andfetching the write data starts one clock after the column address/writecommand cycle.

(5) Precharge Command (Pr)

This is a command for starting the precharging operation for the memorybank selected by A12 and A13, and is instructed by the signals /CS,/RAS, /WE=low level and by the signal /CAS=high level.

(6) Auto Refresh Command

This is a command necessary for starting the automatic refresh, and isinstructed by the signals /CS, /RAS, /CAS=low level, and by the signals/WE, CKE=high level.

(7) No Operation Command (Nop)

This is a command instructing not to substantially carry out theoperation, and is instructed by the signal /CS=low level and by thesignals /RAS, /CAS, /WE=high level.

In the DDR SDRAM, when another memory bank is instructed and a rowaddress strobe/bank active command is supplied while a burst operationis executed in one memory bank, the operation of the row address systemcan be carried out in the another memory bank without at all affectingthe operation of the above one memory bank.

Therefore, it becomes possible to start the internal operation inadvance by issuing a precharge command and a row address strobe/bankactive command for a memory bank different from the memory bank in whicha command is being executed so far as the data D0 to D15 do not comeinto collision at the data input/output terminals of, for example, 16bits. The DDR SDRAM of this embodiment executes the memory access in aunit of 16 bits as described above, possesses addresses of about 4 Mrelying upon addresses A0 to A11, has four memory banks and, hence,possesses the storage capacity of a total of about 256 megabits (4M×4banks×16 bits).

Described below is the detailed reading operation of the DDR SDRAM. Thesignals such as chip select signals /CS, /RAS, CAS and write enablesignal /WE are input in synchronism with the CLK signals. The rawaddress and the bank select signal are input simultaneously with /RAS=0,and are held by the row address buffer 205 and by the bank selectcircuit 212, respectively. A row decoder 210 of a bank designated by thebank select circuit 212 decodes the row address signal, and the data ofthe whole row are output as very small signals from the memory cellarray 200. The very small signals that are output are amplified and heldby the sense amplifier 202. The designated bank becomes active.

After 3CLK from the input of the row address, the column address and thebank select signal are input simultaneously with CAS=0, and are held bythe column address buffer 206 and the bank select circuit 212. When thedesignated bank is active, the column address that is held is outputfrom the column address counter 207, and the column decoder 203 selectsthe column. The selected data are output from the sense amplifier 202.Here, the data are output in an amount of two sets (8 bits in the ×4constitution and 32 bits in the ×16 constitution).

The data output from the sense amplifier 202 are sent out of the chipthrough the data output circuit 211. The output timing varies insynchronism with both the rising and breaking edges of QCLK output fromthe DLL 214. Here, the data of two sets are subjected to the parallelserial conversion to form data of one set ×2. The data strobe signal DQSis output from the DQS buffer 215 simultaneously with the output ofdata. When the burst length preserved in the mode register 213 is notshorter than 4, the address in the column address counter 207 isautomatically increased to read the data of the next column.

The DLL 214 has the role of forming operation clocks QCLK for the dataoutput circuit 211 and for the DQS buffer 215. The data output circuit211 and the DQS buffer 215 require a time before producing the datasignal and the data strobe signal after the internal clock signal QCLKformed by the DLL 214 is input. By advancing the phase of the internalclock signal QCLK to be in advance of the external CLK by using areplica circuit that will be described later, therefore, the phases ofthe data signal and of the data strobe signal are brought into agreementwith that of the external clock CLK. In this case, therefore, the datasignal and the data strobe signal are the ones that are brought fortheir phases into agreement with the external clock signal.

FIG. 7 is a block diagram illustrating the whole DLL according to theembodiment of the invention. FIG. 7 illustrates the whole DLL with theDLL digital unit 4 as a center. The DLL digital unit 4 so controls theDLL analog unit 3 that the external clock signal ECLK_T input throughthe clock input circuit 2091 and the internal clock signal ICLK arebrought in phase with each other.

In order to prevent harmonic locking in the DLL of this embodiment, thefrequencies of the external clock signals ECLK_T and of the internalclock signals ICLK are divided into one-fourth through thefrequency-dividing circuit 401, respectively. The ECLK4 obtained bydividing the frequency of the external clock signals ECLK_T intoone-fourth and the ICLK4 obtained by dividing the frequency of theinternal clock signals ICLK into one-fourth are compared for theirphases by a phase comparator 402. Upon looking at the waveform ofEARLY_INT which is the result of comparison of phases, a state controlcircuit 403 produces a signal TURBO and a signal TURBO1. Apulse-generating circuit 404 produces an up signal UP and a down signalDOWN to control the operation of the charge pump provided in the DLLanalog unit 3.

This embodiment is provided with a charge pump test pulse generatingcircuit 405. A signal CP_PULSE that will be described later and isproduced by this circuit controls the operation of the charge pump inthe DLL analog unit 3 instead of the up signal UP and the down signalDOWN to execute the testing thereof. To simplify the drawing, controlsignals that are not directly related to the invention are not shown.

The frequency-dividing circuit 401 is supplied with clock signals ECLK_Tthrough the clock input circuit 2091 and internal clock signals ICLKthrough the replica delay 406. Therefore, the ECLK4 and the ICLK4obtained by dividing their frequencies into one-fourth are compared fortheir phases by the phase comparator 402. The replica circuit 406 is adelay circuit constituted by the same circuit as the data output circuit211 or the DQS buffer (output circuit) 215. Since the DLL analog unit 3forms an internal clock signal QCLK of a phase advanced by the clockinput circuit 2091 or by the data output circuit 211 (or DQS buffer215), the external clock signal CLK_T becomes in phase with, forexample, the data signal that is received through the data outputcircuit 211 or the clock signal output through the DQS buffer 215.

FIG. 8 is a diagram illustrating the variable delay circuit included inthe DLL analog unit 3 according to the embodiment. The variable delaycircuit 303 is constituted by a variable delay element and a biascircuit. A variable delay element has a constitution in which twodifferential inverters are connected in series, and varies the amount ofdelay by controlling the current of the current source based upon NBIAS.There has been shown a circuit of the two differential inverters.Described below is a circuit of the preceding stage to which the circuitmarks are attached. N-channel MOSFETs Q7 and Q8 are arranged in parallelbetween a common source of the n-channel differential MOSFETs Q1, Q2 andthe ground potential of the circuit, to form a variable current sourcewhich changes the current based upon the NBIAS.

P-channel MOSFETs Q3 and Q4 which are diode-connected, are provided as aload circuit between the drains of the differential MOSFETS Q1, Q2 andthe power-source voltage VDD. To steepen a change in the differentialoutput signal, further, p-channel MOSFETs Q5 and Q6 of a latch form inwhich the gates and drains are connected to each other, are provided inparallel with the diode-connected MOSFETs Q3 and Q4. The drain outputsof the differential MOSFETs Q1 and Q2 are supplied to the gates of thedifferential MOSFETs as an input signal of the circuit of the nextstage. The above two differential inverters are connected in cascade inplural stages to form the variable delay circuit 303. Among them, pluralstages of from 0 to N from the final stage are provided with output tapsTAPN0, TAPP0 to TAPNN, TAPPN. In the embodiment of FIG. 2, there areprovided six output taps.

The bias circuit converts the control voltage VB into a current signalthrough a MOSFET Q9 and connects it to power-source MOSFETs in thedifferential inverters using a simple current mirror circuit. Here,however, a buffer circuit may be used for correcting the controlvoltage-delay amount characteristics. As described above, the variabledelay circuit is provided with plural (e.g., six sets of) output taps.Among them, one output is selected to change the number of stages of thevariable delay circuit.

FIG. 9 is a diagram illustrating the charge pump circuit included in theDLL analog unit 3 according to the embodiment. In order to shorten thelock-in cycle of DLL, the charge pump circuit of this embodimentincludes a current source for a small delay mode constituted by ap-channel MOSFET Q11 which is supplied with a signal ENB through thegate thereof, a current source for an intermediate delay modeconstituted by an n-channel MOSFET Q22 supplied with a signal TURBOthrough the gate thereof, a current source for a large delay modeconstituted by a p-channel MOSFET Q21 supplied with a signal TURBO1through the gate thereof, current mirror biases Q12 to Q20 fortransmitting the current of the current source for the small delay mode,and bidirectional switches Q23 to Q26.

In a state where the signal ENB has the high level, ENT has the lowlevel and DLL is not in operation, the switching MOSFETs Q15 and Q16 areturned off, the switching MOSFETs Q17 and Q18 are turned on, theoperation of the current source for the small delay mode is halted andthe operation of the current mirror circuit is halted, to carry out theoperation consuming a small amount of electric power. In this case, theMOSFETs Q22 and Q21 are turned off due to the signals TURBO and TURBOB.The high-speed lock-in cycle operation using three current sources,i.e., current source for the small delay mode, current source for theintermediate delay mode and the current source for the large delay modewill be described later by using a diagram of waveforms.

FIG. 10 is a circuit diagram illustrating an embodiment of the outputamplifier included in the DLL analog unit 3. The output signal of thevariable delay circuit using the differential inverter shown in FIG. 8is small unlike that of VDD. Therefore, the amplitude must be amplifiedinto a full amplification of the operation voltage like that of VDD.Therefore, an output amplifier 305 must be used. The output amplifier isconstituted by two sets of a combination of a current mirror amplifierconstituted by MOSFETs Q30 to Q35 and a clocked inverter constituted byMOSFETs Q37 to Q40. The current mirror amplifier operates when thecontrol signals are ENT=VDD, ENB=0 (VSS or GND), and the output becomesvalid. When ENT=0 and ENB=VCC, however, the current mirror amplifierdoes not operate and the output assumes a high impedance.

In FIG. 2, the outputs of the six output amplifiers are connected incommon. Among the six output amplifiers, however, only one produces aneffective output due to the signals ENT and ENB, and the number ofstages of the variable delay circuit is changed over in addition to thesignal amplification.

FIG. 11 is a circuit diagram illustrating an embodiment of the controlvoltage-fixing circuit included in the DLL analog unit 3. A value of thecontrol voltage must be given from an external unit at the time ofmeasuring the control voltage—delay amount characteristics of thevariable delay circuit. The control voltage must be fixed by using aprobe from the external side. However, no bulky device is needed if thecharacteristics can be measured without probe. Besides, the measurementcan be taken (packaging, mounting, etc.) to meet the practicalconditions, and no noise enters through the probe.

The control voltage-fixing circuit is constituted by switching MOSFETsQ50 to Q52, voltage-dividing resistor circuit and bidirectional switch.When the signal ON becomes VDD, the MOSFET Q52 is turned on, a currentflows into the series resistance circuit, and voltages V0 to V6 appeardue to the division of voltage by the resistors. Among the signals SETOto 6, only one is set to the high level like VDD, only one of thebidirectional switches is turned on, and the voltages V0 to V6 areconnected to the control voltage VB to fix the control voltage VBrelative to the variable delay circuit.

FIG. 12 is a diagram of waveforms illustrating the operation of theclock-generating circuit according to the invention. When the DLL isreset, the initial phase error takes place on the advancing side.Therefore, a charge-down control starts in the large delay mode. In thelarge delay mode, the phase error is advancing and, hence, the output ofthe phase comparison assumes a high level, and two charge-up controlsignals are formed for one time of phase comparing operation. Due to thecharge-up control signal, the phase error steeply changes toward thetarget value.

If described with reference to the circuit of FIG. 9, the signal TURBO1Bassumes the low level, and the p-channel MOSFET Q21 is turned on to flowa large current. Accordingly, the n-channel MOSFET Q24 and the p-channelMOSFET Q26 are turned on due to the high level of down signal DOWN andthe low level of DOWN_B, and the control voltage VB increases stepwiserelative to the signals DOWN and DOWM_B. In response to the rise in thecontrol voltage VB, the current formed by the P-channel MOSFET Q9 ofFIG. 8 decreases, whereby the operation current of the differentialinverter constituting the variable delay circuit decreases, the delaytime increases, and the phase is changed toward the delay side.

When the phase error exceeds 0 which is a target value, the mode ischanged over to the intermediate delay mode. In the large delay mode,the charge-down control operation only is executed. Therefore, thecharge-up control operation only is executed in the intermediate delaymode. Accordingly, neither the charge-up current source for the largedelay mode nor the charge-down current source for the intermediate delaymode has been provided unlike the embodiment of FIG. 9. Depending uponthe manner of-imparting the initial phase error, these two currentsources may become necessary. In that case, these two current sourcesmust be provided.

If described with reference to the circuit of FIG. 9, to correct thephase error that has increased in excess of delay error 0 due to thelarge delay mode, the signal TURBO assumes the high level, and then-channel MOSFET Q22 is turned on to flow an intermediate current. Tocorrect the delay, therefore, the output of phase comparison assumes thelow level. Due to the high level of the up signal UP and low level ofUP-B formed thereby, therefore, the N-channel MOSFET Q23 and thep-channel MOSFET Q25 are tuned on, to stepwisely decrease the controlvoltage VB in response to the signals UP and UP_B. In response to thedrop in the control voltage VB, the current formed by the p-channelMOSFET Q9 of FIG. 8 increases, whereby the operation current of thedifferential inverter constituting the variable delay circuit increases,and the delay time decreases to correct a delay in the phase.

When the phase error exceeds 0 which is a target value due to theintermediate delay mode, the mode is changed over to the small delaymode. In the small delay mode, the charge-up control operation and thecharge-down control operation based on a small current formed by theMOSFET Q11 are executed depending upon the output of phase comparison.In this case, two pulses (UP/DOWN) are not formed for the result of onetime of phase comparison unlike the large delay mode or the intermediatedelay mode but, instead, one pulse is generated. In the small delaymode, therefore, the error component for the phase error 0 is minimized.

In this embodiment, there exist current sources and bias circuits thatare not required depending upon the mode such as large delay mode orintermediate delay mode. Therefore, the circuit is turned on and off bya signal TURBO, a signal TURBO_B, a signal TURBO1, a signal TURBO1_B, asignal ENT and a signal ENB. The signals have the following values intheir respective modes. The power-off mode is the one for suppressingthe consumption of electric current by halting the operation of thecharge pump.

TURBO TURBO_B TURBO1 TURBO1_B ENT ENB Large VDD 0 VDD 0 VDD 0 modeInter- VDD 0 0 VDD VDD 0 mediate mode Small 0 VDD 0 VDD VDD 0 mode Off 0VDD 0 VDD 0 VDD mode

In the DLL of this embodiment, the initial phase error necessarilyappears on the advancing side in order to minimize the delay time of thevariable delay circuit immediately after it is reset. In order toquickly bring the initial phase error near to the phase error 0immediately after the resetting, the large delay mode is assumed toincrease the phase control amount delay from when the phases arecompared until when the phases are compared next time. In order toincrease the phase control quantity, further, the control operation isexecuted twice in addition to increasing the current of the charge pump.Since the initial phase error appears on the advancing side, the phasecomparator produces an output of the high level such as VDD. When thecontrol operation is executed several times in the large delay mode, thephase error over-shoots in excess of 0. The output of the phasecomparator changes into 0 at a moment when the phases are compared nexttime after the over-shooting.

At this moment, the mode shifts from the large delay mode to theintermediate delay mode.

In the intermediate delay mode, the current of the charge pump isslightly squeezed but the number of times of control operation is notchanged. When the control operation is executed several times in theintermediate delay mode, the phase error exceeds 0 again, which is theunder-shooting. The output of the phase comparator changes into VDD at amoment when the phases are compared next time after the under-shooting.At this moment, the mode shifts from the intermediate delay mode to thesmall delay mode. In the small delay mode, the current of the chargepump is squeezed and the number of times of control operation isdecreased to one time. Thus, the amount of delay control becomes aminimum through the phase comparison of one time. After the phase errorhas exceeded 0 in the small delay mode, the charge-down control signaland the charge-up control signal are output nearly alternatingly, andthe phase error vibrates near 0. This state is a locked-in state.Therefore, if attention is given to the output waveforms only of thephase comparator, the period from when DLL is reset to when the outputof the phase comparator has shifted from VDD to 0 twice becomes alock-in cycle.

This embodiment deals with a new drive system for a charge pump in theanalog control circuit. This system eliminates insensitive band which isa defect of PFD in the conventional drive system and shortens thelock-in cycle. The insensitive band is realized by a simple controlmethod according to which the advance and delay only of the phase arejudged by a phase comparator, the control voltage VB is changed asdescribed above based upon the output of phase comparison, and thedelaying amount is changed in the reverse direction at a moment when thetarget value which is the phase error 0 is exceeded. The insensitiveband varies depending upon the performance of the transistors and thewiring lengths. Upon eliminating the insensitive band, therefore, it isallowed to easily design a circuit that is not affected by the processor the layout.

FIG. 13 is a diagram of waveforms illustrating an example of operationof the clock-generating circuit according to the invention. In thisembodiment, the lock-in takes place in a constant delay system. In FIG.12, the charge-down control signal and the charge-up control signal wereoutput nearly alternatingly. Since the charge pump is an analog circuit,it is not allowed to bring the charge-up amount and the charge-downamount into correct agreement with each other. Therefore, there exists asmall amount of unbalance between the delay(down) and the delay(up) asshown. This unbalance causes an increase in the phase error with thepassage of time and, finally, causes the control signal of one side tobe output twice consecutively (production of control signals two timesconsecutively). The intensity of jittering becomes 2×delay. Though thediagramed embodiment has dealt with the case of delay(down) delay(up),the same holds even for the reverse case.

FIG. 14 is a diagram illustrating the transition of states of the statecontrol circuit included in the clock-generating circuit according tothe invention. The state control circuit 403 is included in the DLLdigital circuit unit of FIG. 7 and forms signals TURBO and TURBO1 thatare supplied to the DLL analog unit 3. In the case of DLL_EN=0 V (VSS),a state for halting the DLL is assumed. When DLL_EN=VDD, the followingstate control operation is executed while looking at a change in thephase comparison output EARLY_INT output from the phase comparator 402:

ΔLarge delay mode TURBO = VDD TURBO1 = VDD ΔIntermediate delay modeTURBO = VDD TURBO1 = 0 ΔSmaLL delay mode TURBO = 0 TURBO1 = 0

FIG. 15 is a circuit diagram illustrating the phase comparator and thestate control circuit according to the embodiment. As shown, the phasecomparator 402 may be a generally employed flip_flop circuit. The phasecomparison output EARLY_INT becomes VDD when the internal clock signalICLK4 rises earlier than the external clock signal ECLK4, and the phasecomparison output EARLY-INT becomes 0 (low level) when the externalclock signal ECLK4 rises earlier than the internal clock signal ICLK4.

The state control operation is such that when the signal DLL_EN is 0,all flip-flop circuits are set to VDD (high level). Thereafter, everytime when EARLY_INT changes, the outputs Q of the flip-flop circuits FF2to FF4 become 0, successively, to produce signals TURBO and TURBO1. Whenthe final signal LOCK becomes VDD, it can be judged that DLL has shiftedinto the locked state.

FIG. 16 is a diagram illustrating an embodiment of the pulse-generatingcircuit. The pulse-generating circuit 404 generates signals UP and DOWNbased upon the phase comparison output EARLY-INT. The pulse-generatingcircuit 404 is capable of producing pulses maintaining a stable pulsewidth upon maintaining synchronism with ECLK_T but is not capable ofproducing pulses shorter than the clock period. The ECLK2 is a signalobtained by dividing the frequency of ECLK_T by two.

FIG. 17 is a diagram illustrating the pulse-generating circuit accordingto another embodiment. In this embodiment, a delay circuit is used toproduce pulses of any desired width. When the width of the pulse is toonarrow, the initial phase error is drawn being lagged behind. Therefore,the pulse width is set to be “phase difference+3.0 ns”. In thepulse-generating circuit of this embodiment, delay is not constant.However, what is important in controlling the delay to be constant isthat delay 0 even at a point of phase difference=0, and there exists noproblem.

FIG. 18 is a diagram illustrating an embodiment of the 1/4 frequencydivider circuit. The 1/4 frequency divider circuit of this embodiment isthe 1 ck lock−2 ck lock change-over type. The DLL of this embodimentemploys 2 ck lock. Therefore, the frequencies of ECLK_T and ICLK must bedivided into one-fourth prior to comparing the phases, in order toprevent harmonic lock. Therefore, when the ECLK_T and ICLK have the samephases, the circuit is so reset that the phase of ICLK4 is in advance ofECLK4 by 720 degrees.

Thereafter, the variable delay circuit and the replica circuit (replicadelay) work to delay the phase of ICLK by 720 degrees (2 ck), so thatECLK 4 and ICLK4 are in phase and are locked together. When the phase ofthe ICLK4 is advancing by 360 degrees instead of 720 degrees, 1 cklocking is effected. It is thus allowed to effect the 1 ck locking and 2ck locking using one circuit. Unlike the general flip-flop circuit, theflip-flop circuit used for the 1/4 frequency divider is provided withboth a set terminal and a reset terminal. Due to the signal 1 CK_LOCK,the phase can be changed right after the reset signal has broken.Described below are changes in the phase right after the resetting dueto changes in the 1 CK_LOCK.

Value of CK_LOCK Phase of ECLK4 Phase of ICLK4 0 0° −720° 1 0° −360°

FIG. 19 is a diagram illustrating an embodiment of the charge pump testpulse-generating circuit. The DLL of the analog control system makes itdifficult to test the state of the internal circuit from the outer sidecompared to that of the digital control system. The operation of thecharge pump is one of the difficulties. The pulse-generating circuit isnecessary for testing to what extent the delay amount of the variabledelay circuit changes when the charge pump is operated one time. Thecharge pump test pulse-generating circuit produces pulses CP-PULSE(having a width of tCK/2) of a number set by CP-SET0-3. Upon operatingthe charge pump with these pulses, it is allowed to test the operationof the charge pump by the externally set CP-SET0-3. The pulse CP-PULSEis produced as the signal PULSEEN assumes the high level.

FIG. 20 is a plan view illustrating a relationship between the memorychip and the lead frame in the semiconductor integrated circuit deviceaccording to an embodiment of the invention. The memory chip has severalVDD and VSS pads, and VDD_DLL and VSS_DLL are among them. However,dedicated bonding pads and lead frames are assigned to VDD_DLL andVSS_DLL to prevent the infiltration of noise from the power sourcewiring.

FIG. 21 is a diagram of an electrostatic protection circuit in thesemiconductor integrated circuit device according to the embodiment ofthe invention. In this embodiment, provision is made of the dedicatedpads VDD_DLL and VSS_DLL for applying operation voltages to the DLL ofthe variable delay circuit. The dedicated pads VDD_DLL and VSS_DLL areprovided with the following elements to cope with ESD.

A diode D70 and a diode-connected MOSFET Q70 are connected in parallelbetween the pad VDD_DLL and the VSS wiring, and diode-connected MOSFETsQ71 and Q72 are connected in parallel between the pad VDD_DLL and thewiring VDD. Similarly, diodes D72 and D73 are connected in parallelbetween the pad VSS_DLL and the wiring VSS, and a diode connected MOSFETQ73 and a diode D71 are connected in parallel between the pad VSS_DLLand the wiring VDD.

As described above, the-semiconductor integrated circuit device isprovided with an electrostatic protection circuit to prevent theinternal elements from being broken down by the static electricitygenerated during the handling such as transportation or assembling ofthe device. Therefore, the power source pads VDD_DLL and VSS_DLL thatare independently formed as described above, are electrically connected,via the electrostatic protection circuit, to the VDD and VSS that supplyoperation voltages to other internal circuits in a broad sense or intheory.

In a state where the semiconductor integrated circuit device isordinarily operated, however, no current flows into the electrostaticprotection circuit, and it cannot be said that it is in an electricallyconnected state. That is, the power-source noise generated in VDD andVSS and fluctuation in the voltage are not transmitted to VDD-DLL orVSS_DLL. From the standpoint of operation of the clock-generatingcircuit of the invention, therefore, it can be said that VDD and VSS areelectrically isolated from VDD_DLL and VSS_DLL.

Described below are the actions and effects obtained from the aboveembodiment.

(1) A semiconductor integrated circuit device having a clock-generatingcircuit that includes a control circuit for forming internal clocksignals by comparing a signal obtained by delaying, through a variabledelay circuit, an input clock signal input through an external terminalwith the input clock signal, and so controlling the delay time of thevariable delay circuit that they are brought into agreement with eachother, wherein in the clock-generating circuit, the element-formingregion constituting the variable delay circuit and the circuit forforming the delay control signals is electrically isolated from theelement-forming region constituting the digital circuit on the samesemiconductor substrate relying upon the element isolation technology,in order to realize a highly precise phase synchronization based on astable delaying operation without affected by a change in the substratepotential caused by the operation of the digital circuit.

(2) In addition to the above, the device is realized through a simpleproduction process in which the circuits such as variable delay circuitand charge pump circuit are formed on a triple well, i.e., on a wellregion of a second type of electric conduction that is deeply formed,and on a well region of a first type of electric conduction or of thesecond type of electric conduction shallowly formed on a commonsemiconductor substrate of the first type of electric conduction,establishing an element isolation technology.

(3) In addition to the above, the variable delay circuit and the chargepump circuit are operated on an operation voltage via dedicated bondingpads and leads different from the power-source terminals for supplyingthe operation voltages to the digital circuits, in order to realize ahigh degree of precision based on the stable delay operation of thevariable delay circuit affected by neither the power-source passage nora fluctuation in the voltage.

(4) In addition to the above, a MOS capacitor element is formed in theperiphery of the well region of the second type of electric conductionthat is deeply formed, and is used for stabilizing the operationvoltage. This makes it possible to absorb noise transmitted through thecommon power source feeder line on the side of the substrate mountingthe semiconductor integrated circuit device and, hence, to realize ahigh degree of precision based on the stable delay operation of thevariable delay circuit.

(5) In addition to the above, provision is further made of a clock inputbuffer for receiving input clock signals that are fed to the variabledelay circuit and a clock output buffer for producing delay signals, theclock input buffer and the clock output buffer being formed on the wellregion of the second type of electric conduction that is deeply formed.Therefore, the variable delay circuit and the delay control signalthereof are not affected by noise included in the signal transmissionpassages, and a high degree of precision is realized based on the stabledelay operation of the variable delay circuit.

(6) In addition to the above, a first frequency-dividing circuit fordividing the frequency of the input clock signals is reset at the startof operation of the clock-generating circuit, and a secondfrequency-dividing circuit for dividing the frequency of the internalclock signals selects either a clock signal delayed by two clocks or aclock signal delayed by one clock behind the external clock that is inphase upon selectively giving a predetermined initial value.

(7) In addition to the above, the first and second frequency-dividingcircuits, the replica delay circuit and the phase comparator circuit areformed in an element-forming region electrically isolated from theelement-forming region where the variable delay circuit and a circuitfor forming delay control signals are formed. This prevents power-sourcenoise generated in the digital circuit operating with its full amplitudefrom being transmitted to the analog circuit unit, and a high degree ofprecision is realized based on the stable delay operation of thevariable delay circuit.

(8) In addition to the above, the clock-generating circuit is mounted ona dynamic RAM which includes plural word lines connected to the addressselection terminals of plural dynamic memory cells, plural pairs ofcomplementary bit lines connected to plural dynamic memory cells, andsense amplifiers constituted by plural latch circuits that are servedwith an operation voltage corresponding to the operation timing signalsto amplify signals of the pairs of bit lines, wherein the variable delaycircuit constituting the clock-generating circuit and a circuit forforming the delay control signals thereof are supplied with operationvoltages through dedicated bonding pads and leads different from thepower-source terminals for supplying the operation voltages to the senseamplifier, in order to realize a high degree of precision based on thestable delay operation of the variable delay circuit without affected bylarge noise from the sense amplifier.

(9) A semiconductor integrated circuit device having a clock-generatingcircuit that includes a control circuit for forming internal clocksignals by comparing a signal obtained by delaying, through a variabledelay circuit, an input clock signal input through an external terminalwith the input clock signal, and so controlling the delay time of thevariable delay circuit that they are brought into agreement with eachother, wherein in the clock-generating circuit, at least the variabledelay circuit is supplied with an operation voltage through dedicatedbonding pads and leads different from the operation voltage feed passageof the digital circuit formed on the same substrate, in order to realizea highly precise phase synchronization based on a stable delayingoperation without affected by a change in the power-source voltagecaused by the operation of the digital circuit.

(10) In addition to the above, the clock-generating circuit is mountedon a dynamic RAM which includes plural word lines connected to theaddress selection terminals of plural dynamic memory cells, plural pairsof complementary bit lines connected to plural dynamic memory cells, andsense amplifiers constituted by plural latch circuits that are servedwith an operation voltage corresponding to the operation timing signalsto amplify signals of the pairs of bit lines, wherein the variable delaycircuit constituting the clock-generating circuit is supplied with anoperation voltage through dedicated bonding pads and leads differentfrom the power-source terminals for supplying the operation voltages tothe sense amplifier, in order to realize a high degree of precisionbased on the stable delay operation of the variable delay circuitwithout affected by large noise from the sense amplifier.

(11) In addition to the above, the digital circuit is provided with aninput circuit for receiving input signals supplied through an externalterminal and an output circuit for sending output signals to theexternal terminal, the input circuit and the output circuit are suppliedwith operation voltages through dedicated bonding pads and leadsdifferent from the power-source terminals for supplying the operationvoltages to the clock-generating circuit and to the sense amplifier, inorder to accomplish stable delaying operation of the variable delaycircuit and sense amplifier operation without permitting theclock-generating circuit and the sense amplifier to be affected by largenoise from the output circuit.

(12) Provision is made of a clock-generating circuit that includes acontrol circuit for forming internal clock signals by comparing a signalobtained by delaying, through a variable delay circuit, an input clocksignal input through an external terminal with the input clock signal,and so controlling the delay time of the variable delay circuit thatthey are brought into agreement with each other, wherein the controlcircuit controls the variable delay circuit so as to return the delayingamount in the reverse direction at a moment when the variable delay timehas exceeded a target value. This eliminates the insensitive band thatis the defect of PFD of the conventional drive system. Upon eliminatingsuch an insensitive band, the phase difference is not affected by theperformance of the transistors or by the wiring lengths, facilitatingthe designing.

(13) In addition to the above, the amount of change in the delay time ofthe variable delay circuit is set nearly constant by the phasecomparator circuit for every phase comparing operation, making itpossible to suppress the error of phase to two folds at the greatest inthe locked-in state.

(14) Upon varying the amount of change in the delay time of the variabledelay circuit by the phase comparator circuit for every phase comparingoperation depending upon the operation conditions, it is allowed torealize an optimum response and stability depending upon the operationconditions.

(15) In addition to the above, the amount of change in the delay time ofthe variable delay circuit is set to be large during a first period offrom the start of operation of the clock-generating circuit until thetarget value is exceeded, is set to be smaller than the amount of changein the delay time in the first period during a second period of from thefirst period until when the delay time becomes smaller than the targetvalue, and is set to be smaller than that in the second period after thesecond period. This makes it possible to stabilize the operation in thelocked-in state while shortening the lock-in cycle from the start of DLLoperation until locking-in.

(16) In addition to the above, the amount of change in the delay time ofthe variable delay circuit decreases every time when the delay time ofthe variable delay circuit exceeds a target value within a range inwhich the phase-synchronizing operation is not lost. This makes itpossible to stabilize the operation in the locked-in state whileimproving the response characteristics.

(17) In addition to the above, the phase comparator circuit forms aphase comparison signal of a high level or a low level in response tothe phase difference, and forms a pulse signal for flowing a charge-upcurrent or a discharge current to the charge pump circuit in response tothe phase comparison signal. This makes it possible to change over theresponse depending upon the pulse output from the pulse-generatingcircuit yet simplifying the circuit.

(18) In addition to the above, the amount of delay time of the variabledelay circuit can be flexibly varied based on the combination of thenumber of pulse signals and the charge current of the charge pumpcircuit that varies depending upon the pulse signals, by using a simplecircuit to realize a desired response maintaining stability in theoperation.

In the foregoing was concretely described the invention accomplished bythe present inventors by way of embodiments. It should, however, benoted that the invention of this application is in no limited to theabove embodiments only but can be changed in a variety of other wayswithout departing from the gist of the invention. For example, the DLLmay be a digital control digital DLL or a digital control analog DLL.Even in the variable delay circuit of these DLL, the voltage supplied tothe gate of the MOSFET changes with a change in the power source voltagewhereby a current that flows undergoes a change. As the substratevoltage changes, further, the threshold voltage of-the MOSFET changesdepending upon the substrate effect causing the drain current to change.Upon applying the present invention, therefore, a variable delay circuitconstituting the DLL is realized and control signals thereof arestabilized, suppressing the jittering in the clock signals that areoutput.

The technology for electrically isolating the variable delay circuitconstituting the DLL and the circuit for forming the control signalstherefor, may be the one that utilizes the SOI (silicon-on-insulator)structure.

Accompanying an increase in the operation speed of the semiconductorintegrated circuit device, the frequency of the clock signals is everincreasing and the period of a clock is becoming ever short. Therefore,decreasing the jittering which is the fluctuation in the phase of theclock signals results in a reduction in the time margin included in theperiod of one clock, which is very advantageous for increasing thefrequency of the clock signals.

The clock-generating circuit of the invention can be extensively usedfor a variety of digital semiconductor integrated circuit devices thatmount a clock-generating circuit (or reproducing circuit) and hassynchronous inputs and outputs, in addition to the synchronous DRAMdescribed earlier.

Briefly described below are the effects obtained by the representativeexamples of the invention disclosed in this application. A semiconductorintegrated circuit device having a clock-generating circuit thatincludes a control circuit for forming internal clock signals bycomparing a signal obtained by delaying, through a variable delaycircuit, an input clock signal input through an external terminal withthe input clock signal, and so controlling the delay time of thevariable delay circuit that they are brought into agreement with eachother, wherein in the clock-generating circuit, the element-formingregion constituting the variable delay circuit and the circuit forforming the delay control signals is electrically isolated from theelement-forming region constituting the digital circuit on the samesemiconductor substrate relying upon the element isolation technology,in order to realize a highly precise phase synchronization based on astable delaying operation without affected by a change in the substratepotential caused by the operation of the digital circuit.

A semiconductor integrated circuit device having a clock-generatingcircuit that includes a control circuit for forming internal clocksignals by comparing a signal obtained by delaying, through a variabledelay circuit, an input clock signal input through an external terminalwith the input clock signal, and so controlling the delay time of thevariable delay circuit that they are brought into agreement with eachother, wherein in the clock-generating circuit, at least the variabledelay circuit is supplied with an operation voltage through dedicatedbonding pads and leads different from the operation voltage feed passageof the digital circuit formed on the same substrate, in order to realizea highly precise phase synchronization based on a stable delayingoperation without affected by a change in the power-source voltagecaused by the operation of the digital circuit.

Provision is made of a clock-generating circuit that includes a controlcircuit for forming internal clock signals by comparing a signalobtained by delaying, through a variable delay circuit, an input clocksignal input through an external terminal with the input clock signal,and so controlling the delay time of the variable delay circuit thatthey are brought into agreement with each other, wherein the controlcircuit controls the variable delay circuit so as to return the delayingamount in the reverse direction at a moment when the variable delay timehas exceeded a target value. This eliminates the insensitive band thatis the defect of PFD of the conventional drive system. Upon eliminatingsuch an insensitive band, the phase difference is not affected by theperformance of the transistors or by the wiring lengths, facilitatingthe designing.

We claim:
 1. A semiconductor integrated circuit device comprising: aclock-generating circuit that includes a variable delay circuit forproducing second clock signals by delaying, by a predetermined delaytime, first clock signals that are formed based upon clock signals inputthrough an external terminal, and a control circuit for comparing thephase of third clock signals formed based on the second clock signalswith the phase of the first clock signals and for so controlling thedelay time that the difference between the phases is decreased; and aninternal circuit that operates in response to the second clock signals;which are formed on a common semiconductor substrate; is wherein anelement-forming region constituting the variable delay circuit isisolated from an element-forming region constituting the internalcircuit by using isolated well regions formed on the commonsemiconductor substrate.
 2. A semiconductor integrated circuit deviceaccording to claim 1, wherein: the delay time is controlled by an analogvoltage; the control circuit includes a phase comparator circuit whichcompares the phase of the first clock signals with the phase of thethird clock signals and produces control signals, and a charge pumpcircuit that generates the analog voltage based on the control signals;and the charge pump circuit is electrically isolated from theelement-forming region that constitutes the internal circuit.
 3. Asemiconductor integrated circuit device according to claim 2, whereinthe circuits such as variable delay circuit and charge pump circuit areformed on a well region of a second type of electric conduction that isdeeply formed, and on a well region of a first type of electricconduction or of the second electric conduction shallowly formed on acommon semiconductor substrate of the first type of electric conduction.4. A semiconductor integrated circuit device according to claim 1 or 2,wherein: the semiconductor integrated circuit device has a first supplyunit for supplying a first voltage and a second supply unit forsupplying the first voltage; the internal circuit receives the firstvoltage supplied from the first supply unit; and the variable delaycircuit receives the first voltage supplied from the second supply unit.5. A semiconductor integrated circuit device according to claim 4,wherein a MOS capacitor element is formed in the periphery of a wellregion of the second type of electric conduction that is deeply formed,and is used for stabilizing the first voltage supplied to the variabledelay circuit.
 6. A semiconductor integrated circuit device according toclaim 4, wherein the clock-generating circuit further has a clock inputbuffer that produces the first clock signals upon receiving the inputclock signals, and a clock output buffer that produces fourth clocksignals upon receiving the second clock signals; the internal circuitoperates upon receiving the fourth clock signals; and the clock inputbuffer and the clock output buffer are formed on a well region of thesecond type of electric conduction that is deeply formed.
 7. Asemiconductor integrated circuit device according to claim 1, whereinthe control circuit includes a frequency-dividing circuit that dividesthe frequencies of the first clock signals and of the second clocksignals.
 8. A semiconductor integrated circuit device according to claim1, wherein: the delay time is controlled by an analog voltage; thecontrol circuit includes a first frequency-dividing circuit for formingfifth clock signals by dividing the frequency of the first clocksignals, a second frequency-dividing circuit for forming sixth clocksignals by dividing the frequency of the third clock signals, and aphase comparator circuit for producing control signals by comparing thephase of the fifth clock signals with the phase of the sixth clocksignals, and a charge pump circuit that generates the analog voltagebased upon the control signals; wherein the fifth and sixth clocksignals assume predetermined initial values when the clock-generatingcircuit is in operation.
 9. A semiconductor integrated circuit accordingto claim 1, wherein the semiconductor integrated circuit device furtherincludes: a clock input circuit which receives the input clock signalsand produces the first clock signals; an output circuit that operatesupon receiving the second clock signals; and a replica delay circuit forforming the third clock signals by delaying the second clock signals bythe time corresponding to the delay times of the clock input circuit andof the output circuit; wherein the internal circuit includes the outputcircuit.
 10. A semiconductor integrated circuit device according toclaim 8, wherein the first and second frequency-dividing circuits andthe phase comparator circuit are formed in an element-forming regionelectrically isolated from an element-forming region where the variabledelay circuit is formed.
 11. A semiconductor integrated circuit deviceaccording to claim 1, wherein: the semiconductor integrated circuitdevice has a first supply unit for supplying a first voltage and asecond supply unit for supplying the first voltage; the internal circuitincludes plural word lines connected to address selection terminals ofplural dynamic memory cells, plural pairs of complementary bit linesconnected to the plural dynamic memory cells, and sense amplifiersconstituted by plural latch circuits for amplifying the signals of theplural pairs of complementary bit lines; and wherein the senseamplifiers receive the first voltage supplied from the first supplyunit; and the variable delay circuit receives the first voltage suppliedfrom the second supply unit.
 12. A semiconductor integrated circuitdevice according to claim 5, wherein the clock-generating circuitfurther has a clock input buffer that produces the first clock signalsupon receiving the input clock signals, and a clock output buffer thatproduces fourth clock signals upon receiving the second clock signals;the internal circuit operates upon receiving the fourth clock signals;and the clock input buffer and the clock output buffer are formed on awell region of the second type of electric conduction that is deeplyformed.